def add_highlight(self, field, fragment_size=None,
number_of_fragments=None, fragment_offset=None):
"""Add a highlight field.
The Search object will be returned, so calls to this can be chained.
"""
if self.highlight is None:
self.highlight = HighLighter("<b>", "</b>")
self.highlight.add_field(field, fragment_size, number_of_fragments, fragment_offset)
return self
